Project Summary/Abstract Learning the meaning of number words and the cardinal principle is one of the first steps in children?s developing mathematical abilities, and the age at which children master the cardinal principle is predictive of later mathematical achievement. Children of low socioeconomic status (SES) backgrounds achieve this milestone later than high SES peers contributing to an achievement gap in mathematics. It is therefore critical to develop interventions that facilitate early number word learning, and understanding how the brain changes as children learn the meaning of number words may facilitate this enterprise. The neurocognitive mechanisms that support the acquisition of the verbal count list have not been mapped. Developmental neuroimaging studies reveal important developmental trends in the neural processing of Arabic numerals and nonsymbolic quantities such as a fronto-parietal shift whereby children engage the prefrontal cortex to a greater extent than adults who recruit the intraparietal sulcus (IPS). However, no studies to date have used functional imaging to examine how children?s brains change as they learn the meaning of number words or how individual differences in brain structure and function might influence number word learning or susceptibility to intervention. This proposal seeks to uncover the neurobiological substrates that support the acquisition of the verbal count list, in addition to identifying how individual differences in home environment might shape this process. During the K99 phase, Aim 1 will use fMRI paired with a newly developed number word mapping paradigm to identify brain regions that are engaged when children process the meaning of number words. We will examine whether neural activity in the IPS and frontal regions varies as a function of number word knowledge. Aim 2 will examine differences in resting state functional connectivity and structural connectivity as a function of cardinal principle knowledge. We will test whether the acquisition strengthens connections between the right and left IPS, while connections from the IFG and IPS decrease. For both Aims 1 and 2 we will examine whether SES and home numeracy modulate structural and functional brain interactions with number word knowledge. Finally, in the R00 phase, Aim 3 will employ a brain imaging in-home number word intervention to interrogate learning induced cortical reorganization in low income pre-numerate children. I will implement an intervention designed to facilitate the acquisition of the cardinal principle and simultaneously identify the structural and functional brain changes that accompany number word learning. Additionally, I will examine whether individual differences in brain and behavior predict which children will benefit most from the number word intervention. The results from these studies will elucidate the neural mechanisms involved in learning number words ? an important developmental milestone, which will improve targeted interventions for children from diverse economic backgrounds.